Mesoporous silica catalyst for catalyzing esterification reaction of tricarboxylic acid as well as preparation method and application of mesoporous silica catalyst

Abstract

The invention provides a mesoporous silica catalyst with esterification reaction catalysis performance and a preparation method and application thereof. Relates to the technical field of fine organic chemicals. The surface of the mesoporous silica catalyst contains abundant sulfonic acid groups and can catalyze an esterification reaction of organic carboxylic acid; the particle size of the catalyst is averagely distributed between 0.5 mu m and 2 mu m, the surface of the catalyst is rich in pore size distribution, the most probable pore size is 1-10 nm and 20-100 nm, the specific surface area of the catalyst is ultrahigh due to the special structure, the specific surface area is 302-569 m < 2 > / g, and the heat-resistant temperature is 190 DEG C or above. The catalyst can efficiently catalyze the esterification reaction of organic carboxylic acid and improve the average conversion rate of the organic carboxylic acid, and no obvious side reaction occurs; the mesoporous silica catalyst has high recyclability, and the catalyst can be recycled only through operations such as filtration and centrifugation; meanwhile, the catalyst has the advantages of no equipment corrosion, environment friendliness and the like.

Description

Technical Field

[0001] The invention relates to the technical field of fine organic chemical industry, and in particular to a mesoporous silica catalyst for catalyzing the esterification reaction of tricarboxylic acid, and a preparation method and application thereof. Background Art

[0002] Carboxylic acid esters are an important chemical substance with various physical and chemical properties and excellent characteristics such as low toxicity, which makes them widely used in many fields such as food, cosmetics, and medicine. Carboxylic acid esters are compounds generated by the dehydration of carboxylic acids and alcohols through esterification reactions. Traditional esterification reactions are mainly catalyzed by liquid acids such as concentrated sulfuric acid and hydrochloric acid. However, such liquid acid catalysts have poor selectivity during the reaction and may cause other side reactions such as etherification. After the reaction, alkaline neutralization operations are required. Not only are the neutralization and separation operations more complicated, but they also bring risks of corrosion to production equipment and environmental pollution. At the same time, the recyclability of liquid acids is extremely low. Therefore, catalysts with high selectivity, easy separation, and recyclability for esterification reactions have gradually attracted people's attention.

[0003] Compared with the above liquid acid catalysts, solid acid catalysts such as molecular sieves, heteropoly acids, cation exchange resins, metal salts, etc., are gradually applied to the esterification process of organic carboxylic acids due to their good separation and recyclability. However, solid acids also have some problems, such as:

[0004] (1) The number of active sites provided by solid acid catalysts on their surfaces is insufficient, resulting in low catalytic selectivity and low catalytic efficiency during the reaction, leading to problems such as low production capacity.

[0005] (2) Solid acid catalysts may experience surface chemical group destruction under high temperature conditions, resulting in the ineffectiveness of the solid acid catalytic activity.

[0006] (3) The catalytic performance of some solid acids is sensitive to the presence of an aqueous phase. They are basically used to catalyze the esterification of dibasic organic carboxylic acids, and the catalytic reaction has low universality.

[0007] In view of the above problems, catalysts with biochar or silica as carriers have gradually attracted people's attention due to their advantages of easy synthesis and modification and high stability. Catalysts with biochar or carbon / silicon dioxide composites as carriers have been widely studied, while silica catalysts are still less studied. In addition, in the current patent disclosure technology, most catalysts can only catalyze dibasic organic carboxylic acids, and esterification catalysts for tertiary organic carboxylic acids such as citric acid and aconitic acid are still lacking in research. The reason is that the three carboxyl groups contained in the tertiary organic carboxylic acid have lower reaction activity due to steric hindrance or intramolecular hydrogen bonding, and the difficulty of esterification is higher than that of dibasic carboxylic acids; at the same time, the reaction activity of the three carboxyl groups is different, which will also cause differences in the esterification order. In the report on silica catalysts, patent CN104248979A discloses a spherical mesoporous silica composite carrier and catalyst, its preparation method and application, and a preparation method for ethyl acetate. However, the silica catalyst prepared by this method is only used to catalyze ethyl acetate, and its universality is low.

[0008] Therefore, how to design and produce a type of esterification catalyst with high catalytic activity, easy product separation, high production capacity and green environmental protection for the esterification of tricarboxylic acids has extremely high scientific research value and industrial production application value. Summary of the invention

[0009] In order to solve the defects of existing liquid acid and solid acid catalysts, the purpose of the present invention is to provide a mesoporous silica catalyst for catalyzing the esterification reaction of tricarboxylic acids, and a preparation method and application thereof, so as to expand the types of esterification reaction catalysts and the types of catalytic reactions thereof.

[0010] The purpose of the present invention is achieved through the following technical solutions:

[0011] The first aspect of the present invention provides a mesoporous silica catalyst for catalyzing the esterification reaction of tricarboxylic acids, wherein the catalyst is composed of a mesoporous silica matrix and an organic functional group supported on the surface for surface modification; the particle size distribution of the silica matrix is ​​between 0.5 and 2 μm, and the specific surface area of ​​the silica matrix is ​​302 to 569 m 2 / g, the most probable pore sizes are 1-10nm and 20-100nm, and the heat-resistant temperature is above 190℃.

[0012] The second aspect of the present invention provides a method for preparing a mesoporous silica catalyst for catalyzing the esterification reaction of tricarboxylic acids, comprising the following steps:

[0013] (1) Preparation of mesoporous silica: Using silane as raw material, deionized water as solvent, surfactant as micelle template, and inorganic salt as nucleation modifier, a mesoporous silica solution is obtained by heating and stirring under the catalysis of an alkaline catalyst.

[0014] (2) Purification and modification of mesoporous silica: The mesoporous silica is purified by centrifugal washing to obtain high-purity mesoporous silica, which is then dried. After drying, the mesoporous silica has an average particle size of 0.5-2 μm and a specific surface area of ​​302-569 m 2 / g, and the most probable pore diameters are 1-10nm and 20-100nm. Using deionized water as solvent, the dried mesoporous silica is dispersed in water by ultrasound to obtain a uniform mesoporous silica solution. Subsequently, 3-mercaptopropyltrimethoxysilane is added thereto, and the modified mesoporous silica solution is obtained after heating and reacting for a certain period of time.

[0015] (3) Sulfonation of modified mesoporous silica: hydrogen peroxide is added to the modified mesoporous silica solution to carry out stirring reaction. After the reaction is completed, centrifugation is performed to obtain a centrifuged product, which is placed in an oven at 60° C. to dry to obtain dry sulfonated mesoporous silica powder.

[0016] Preferably, the silane used in the above preparation step (1) includes but is not limited to at least one of ethyl orthosilicate, tetrapropyl orthosilicate, tetrabutoxysilane, methyltriethoxysilane, dimethyldiethoxysilane or ethyl polysilicate, and the amount used is 2.4-3.3wt%.

[0017] More preferably, the silane used in the preparation step (1) is ethyl orthosilicate, and the amount used is 2.5-3.0 wt%.

[0018] In the process of preparing the catalyst matrix, the first step is to form silica micronuclei. After some silane forms micronuclei under the catalytic action of the alkaline catalyst, the remaining silane will gradually adhere to the surface of the micronuclei and hydrolyze, and finally the size of the formed matrix will gradually increase. Therefore, the amount of silane used will directly affect the number of nucleation sites in the solution and the size of the final matrix. The appropriate silane concentration will ensure the stable growth of the subsequent silica matrix while satisfying the nucleation sites, avoiding the problem of too many nucleation sites and small subsequent growth.

[0019] Preferably, the surfactant micelles used in the above preparation step (1) include but are not limited to at least one of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123), polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (F127), hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, and hexadecyltrimethylammonium toluenesulfonate, and the shared amount is 0.15wt%-0.8wt%.

[0020] More preferably, the surfactant micelles used in the above preparation step (1) are polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) and polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (F127), and the shared amount is 0.2-0.4wt%.

[0021] The role of surfactants is micellar agents. The presence of micellar agents has a huge impact on the formation, subsequent growth and structural shaping of the above-mentioned micronuclei. When micellar agents exist, a large amount of micellar agents will be attached to the surface of the micronucleus after it is formed, which will cause the subsequent silane to attach and grow in an inserted manner on the surface of the micronucleus, such as Figure 1 As shown. Since the molecular weight and length of each micellar agent are different, after removing different micellar agents, corresponding morphological structures will be formed. The micellar agents P123 and F127 selected in the present invention are copolymers, and the micelle chains are long and complex, so more silanes can be inserted to make the matrix particle size larger and have a richer pore structure. P123 and F127 are both polymers of the same type, so when used in combination, the particle size and structure can be further improved, and the specific surface area of ​​the silica matrix can be increased.

[0022] Preferably, the inorganic salt used in the above preparation step (1) includes but is not limited to at least one of potassium chloride, sodium chloride, barium chloride, ferric chloride and calcium chloride, and the amount used is 5.0-18.0 wt%.

[0023] More preferably, the inorganic salt used in the above preparation step (1) is sodium chloride, potassium chloride or barium chloride, and the amount used is 5.5-17.2 wt%.

[0024] Inorganic salts, as nucleation modifiers, mainly affect the final particle size by affecting the size of the micronucleus. In the solution, metal ions increase the distance between silanes through the size of the nucleus and the mutual repulsion of electrons, reduce the contact between silanes and form a large number of micronuclei, so that the micronuclei can achieve initial growth. Among them, the larger the diameter and the more charge of the metal ion, the stronger the repulsion, and the larger the initial size of the micronucleus. Sodium chloride, potassium chloride or barium chloride can make the micronucleus stably obtain a larger initial size due to their higher solubility and suitable size, which is conducive to the subsequent micronucleus growth.

[0025] Preferably, in the above preparation step (1), the alkaline catalyst includes but is not limited to aqueous ammonia, triethanolamine, ethylamine, propylamine, butylamine, diethylamine, diethylamine or triethylamine, and the amount used is 22-35wt%.

[0026] More preferably, in the above preparation step (1), the alkaline catalyst is aqueous ammonia, and the amount used is 25-35%.

[0027] The formation of silane micronuclei requires alkaline catalysts to catalyze hydrolysis. The stronger the alkalinity of the alkaline catalyst, the stronger the hydrolysis effect, which will cause a large amount of silane to hydrolyze at the beginning of the reaction, forming a large number of micronuclei and reducing the amount of silane used for subsequent growth. Ammonia water has higher solubility and lower viscosity, and can be distributed more quickly in the system to evenly catalyze the silica preparation process.

[0028] Preferably, in the above preparation step (1), the heating temperature is 60-85° C. and the stirring time is 4-8 h;

[0029] More preferably, in the above preparation step (1), the heating temperature is 65-85° C. and the stirring time is 6-8 h.

[0030] The formation and growth of silane micronuclei are also related to temperature. When the temperature is high, the nucleation rate is fast, which is not conducive to growth, and the reaction time is short. When the temperature is low, the nucleation rate is fast, which is conducive to growth, and the reaction time is long. Therefore, when preparing mesoporous silica matrices of different sizes, the effect of temperature needs to be considered.

[0031] Preferably, in the above preparation step (2), the centrifuge speed is 1000-1800 rpm, the centrifugation time is 5-10 min, the number of centrifugation is 5 times, the detergent is deionized water or ethanol; the blower drying temperature is 50-60°C, and the drying time is 8-12h.

[0032] More preferably, in the above preparation step (2), the centrifuge speed is 1600 rpm, the centrifugation time is 10 min, the detergent is deionized water; the air drying oven temperature is 60° C., and the drying time is 9-10 h.

[0033] After the preparation of the mesoporous silica matrix, it needs to be washed to remove excess surfactant and silane. Since the matrix has a certain weight, it can be separated by centrifugation. The drying time is related to the particle size. The smaller the particle size, the smaller the pore size, so the drying time needs to be increased.

[0034] Preferably, in the above preparation step (2), the mass ratio of mesoporous silica to 3-mercaptopropyltrimethoxysilane is (5-8):1; the reaction temperature is 40-75°C, and the reaction time is 6-10h.

[0035] More preferably, in the above preparation step (2), the mass ratio of mesoporous silica to 3-mercaptopropyltrimethoxysilane is (6-8):1; the reaction temperature is 60-70°C; and the reaction time is 6-8h.

[0036] During the modification, if there is too much modifier, cross-linking may occur between the silica matrices, which is not conducive to subsequent dispersion. Therefore, it is necessary to control the amount of modifier, reaction temperature and reaction time to control the reaction process.

[0037] Preferably, in the above preparation step (3), the amount of hydrogen peroxide is 35-45wt%, the reaction time under heating and stirring is 12-28h, the centrifuge speed is 1000-2000rpm, the centrifugation time is 5-10min, the number of centrifugation is 5 times, the detergent is deionized water or ethanol; the drying temperature after centrifugation is 50-80°C, and the drying time is 8-12h.

[0038] More preferably, in the above preparation step (3), the amount of hydrogen peroxide is 40wt%, the reaction time under heating and stirring is 20-24h, the centrifuge speed is 1600rpm, the centrifugation time is 10min, the detergent is deionized water; the drying temperature after centrifugation is 70°C, and the drying time is 9-11h.

[0039] After the modification is completed, it needs to be oxidized into sulfonic acid groups by hydrogen peroxide solution. Therefore, this process requires more hydrogen peroxide and a longer reaction time to ensure the generation of more sulfonic acid groups; and the generation of sulfonic acid groups is also beneficial to the dispersion of the silica catalyst.

[0040] The third aspect of the present invention also provides the use of the above-mentioned mesoporous silica catalyst in the esterification reaction of tricarboxylic acid.

[0041] The fourth aspect of the present invention also provides a method for preparing a tricarboxylic acid ester, the method also includes a catalyst recovery process, specifically comprising the following steps:

[0042] (1) The above-mentioned mesoporous silica catalyst, tricarboxylic acid and alcohol are mixed.

[0043] Preferably, based on 100 parts by mass of the total mass of the tricarboxylic acid and the alcohol, the amount of the mesoporous silica catalyst added is 0.3-10 parts by mass;

[0044] More preferably, the added amount of the mesoporous silica catalyst is 0.4-8.0 parts by mass.

[0045] Preferably, the molar ratio of the tricarboxylic acid to the alcohol is 1:3-1:8; more preferably, the molar ratio of the tricarboxylic acid to the alcohol is 1:3-1:6.

[0046] Preferably, the tricarboxylic acid is at least one of citric acid and aconitic acid.

[0047] Preferably, the alcohol includes but is not limited to methanol, ethanol, 2-methoxyethanol, 2-ethoxyethanol, propanol, isopropanol, n-butanol, isobutanol, tert-butanol, n-pentanol, isopentanol, tert-pentanol, 2-methylpentanol, 2-methyl-2-pentanol, 2-methyl-3-pentanol, 3-ethyl-3-pentanol, 4-methyl-1-pentanol, 4-methyl-2-pentanol, n-hexanol, 2-hexanol, 3-hexanol, 2- At least one of ethylhexanol, 3,5,5-trimethylhexanol, n-heptanol, 2-heptanol, 3-heptanol, 2-methylheptanol, 4-methyl-3-heptanol, 3-propylheptanol, 2,6-dimethyl-4-heptanol, n-octanol, 2-octanol, n-nonanol, 2-nonanol, 3-nonanol, 5-ethyl-2-nonanol, 2,6,8-trimethyl-4-nonanol, n-decanol, isodecyl alcohol, n-undecanol, and n-dodecanol.

[0048] More preferably, the alcohol is any one of methanol, butanol, 2-ethylhexanol, n-octanol, and dodecanol.

[0049] In the esterification reaction, the molecular structure of acids and the molecular chain length of alcohols can significantly affect the speed of the reaction. Tricarboxylic acids have a certain difficulty in esterification due to their obvious steric effect, and long-chain alcohols (more than C8) can further increase the difficulty of esterification, which requires catalysts to have higher catalytic activity and dispersibility. Since the sulfonated mesoporous silica of the present invention has flexible particle size distribution and abundant active groups, the active groups make it have better dispersibility, so it can be more effectively catalyzed esterification. After verification, the above ratio can avoid or reduce the waste of other raw materials, greatly improving the economy of production.

[0050] (2) The mixed system is then heated to react, wherein the heating temperature is 50-170° C.; the reaction time is 4-14 hours; and the separation operation includes at least one of static sedimentation, centrifugation, suction filtration, and filtration.

[0051] Preferably, the heating temperature is 68-150° C., and the reaction time is 4-10 h.

[0052] More preferably, the heating temperature is 100-145° C., and the reaction time is 4-8 h.

[0053] When the temperature is lower than 68°C, the water produced by esterification cannot be discharged from the system faster, so the efficiency of the esterification reaction will be greatly reduced, and it will take longer to obtain the corresponding yield; when the temperature is higher than 150°C, some alcohol raw materials will leave the system, which will also affect the reaction rate. Therefore, only at this temperature, the overall reaction rate of aconitate is high and the yield is stable.

[0054] (3) After the reaction, a separation operation is performed to separate the sulfonated mesoporous silica from the reaction system.

[0055] Preferably, the separation operation is filtration. Since the sulfonated mesoporous silica is a solid phase, it can be separated from the reaction system by simple operation and can be used in the next reaction, thus achieving catalyst reuse and higher atom economy.

[0056] In summary, under the action of the catalyst of the present application, the above ratio can not only ensure the esterification reaction efficiency and the conversion rate of the product, but also avoid the situation where the production cost is too high due to excessive raw material consumption.

[0057] Beneficial effects:

[0058] The beneficial effects of this application include but are not limited to:

[0059] 1) Atom economy and recyclability: Compared with traditional liquid strong acid catalysts, sulfonated mesoporous silica catalysts have high catalytic selectivity and no obvious side reactions, which avoids the corrosion of liquid strong acid catalysts on reaction equipment. At the same time, the simple physical recovery process also avoids the complex post-processing process and waste discharge of traditional catalysts, fully meeting the needs of green and recycling at the production end, and is reusable.

[0060] (2) Controllable size and morphology: Sulfonated mesoporous silica catalysts can effectively control the particle size and morphology of the prepared catalyst by combining different templates and nucleation modifiers through simple temperature and time control to meet the usage requirements in different scenarios.

[0061] (3) Highly efficient and stable catalysis: The catalyst of the present invention has a very high specific surface area and a rich pore structure. This hierarchical structure can load more active groups and improve the uniformity of loading. The large amount of loading of active groups also greatly improves the catalytic efficiency. At the same time, since the active groups are stably covalently bonded to the matrix, the catalyst will not lose its activity at high temperatures, and can continuously, efficiently and stably catalyze the reaction at the production end.

[0062] (3) Universality of application scenarios: In the production of organic carboxylic acid esters, monocarboxylic acids and dicarboxylic acids are easily catalyzed by catalysts due to their high activity. However, due to steric hindrance or intramolecular hydrogen bonding, the three carboxyl groups in tricarboxylic acids have lower reactivity, and the esterification is more difficult than that of dicarboxylic acids. At the same time, the difference in the reactivity of the three carboxyl groups will also lead to differences in the esterification order. Compared with citric acid, aconitic acid in tricarboxylic acids has an additional carbon-carbon conjugated double bond. This conjugated double bond greatly increases the rigidity of the main structure of the aconitic acid molecule, and the molecular chain connected to the double bond is less likely to rotate. Therefore, the mobility of the carboxyl groups around the carbon-carbon double bond is also reduced, and the chance of contact with the catalyst is reduced, making the esterification reaction more difficult. Compared with aconitic acid, citric acid does not contain a carbon-carbon conjugated double bond, and the mobility of the molecular chain is relatively high. The three carboxyl groups contained on it have more opportunities to contact the catalyst. Therefore, the esterification reaction of citric acid is easier to proceed than that of aconitic acid. However, under the tricarboxylic acid esterification system, the catalytic effect of ordinary catalysts cannot guarantee the complete esterification of the three carboxyl groups on the tricarboxylic acid. Therefore, if the catalyst is not selected properly, incomplete esterification will occur, and the product will not only contain tri-esterification products, but also mono-esterification and diesterification products. The sulfonated mesoporous silica catalyst described in the present invention has a flexible and controllable particle size and extremely rich active sites, so that it can more fully contact each carboxylic acid group during the catalytic esterification of aconitic acid, promote its esterification process, and then accelerate the reaction process and improve the conversion rate; and citric acid is easier to carry out esterification reaction and obtain esterification products under this esterification catalytic system because the molecular chain activity is higher. The catalytic universality of the present application also provides a new direction for the industrial production of large sterically hindered organic carboxylates, which can expand and enrich the types of organic carboxylates produced in industry.

[0063] Other features and advantages of the present invention will be described in more detail in the following specific implementation section. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0065] Figure 1 :Insertion growth mechanism (the black part CPB is micellar agent, the red part is silane)

[0066] Figure 2 :SEM images of sulfonated mesoporous silica particles of different sizes

[0067] Figure 3 Example 1 Sulfonated mesoporous silica mapping - Si, O, S element distribution

[0068] Figure 4:Example 1 BET curve of sulfonated mesoporous silica DETAILED DESCRIPTION

[0069] The specific implementation of the present invention is described in detail below. However, it should be noted that the specific implementation described below is only used to illustrate and explain the present invention and should not be construed as limiting the scope of the present invention.

[0070] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0071] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0072] Example 1

[0073] This embodiment provides a 0.5 μm mesoporous silica catalyst and a preparation method thereof. The specific preparation steps are as follows:

[0074] (1) Preparation of mesoporous silica: Taking a 250g reaction system as an example, the amount of tetraethyl orthosilicate in the reaction system is 6.25g (2.5wt%), the amount of surfactant ethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) (purchased from McLean, average Mn ~ 5,800) is 0.5g (0.2wt%), the amount of nucleating modifier sodium chloride is 13.75g (5.5wt%), the amount of alkaline catalyst ammonia water is 87.5g (35wt%), and the rest is deionized water (142g). After stirring for 6h at a heating temperature of 85°C, a mesoporous silica solution is obtained.

[0075] (2) Purification of mesoporous silica: Deionized water was used as detergent, the centrifuge speed was 1600 rpm, the centrifugation time was 10 min, and the centrifugation was performed 5 times in total. After centrifugation, the mesoporous silica was dried in a forced air drying oven at 60° C. for 10 h.

[0076] Mesoporous silica modification: Deionized water was used as solvent, and mesoporous silica and 3-mercaptopropyltrimethoxysilane (mass ratio was 6:1) were added thereto, and the mixture was reacted at a heating temperature of 70° C. for 8 h to obtain a modified mesoporous silica solution.

[0077] (3) Sulfonation of modified mesoporous silica: hydrogen peroxide was added to the above solution for stirring reaction, the amount of hydrogen peroxide added accounted for 40wt% of the total reaction system, and the reaction time was 24h. After the reaction, centrifugation was performed at a speed of 1600rpm, a centrifugation time of 10min, and centrifugation was performed 5 times. The centrifuged product was placed in a 70°C oven and dried for 11h to obtain 0.5μm sulfonated mesoporous silica.

[0078] Example 2

[0079] This embodiment provides a 1 μm mesoporous silica catalyst and a preparation method thereof, and the specific implementation method is the same as that of Example 1; the difference is that:

[0080] In step (1), the amount of tetraethyl orthosilicate is 7.0 g (2.8 wt%), the surfactant is ethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (F127) (purchased from McLean, average Mn ~ 13,000), the amount is 1.0 g (0.4 wt%), the nucleating modifier is potassium chloride, the amount is 24.75 g (9.9 wt%), the amount of ammonia water is 75 g (30 wt%), and the rest is deionized water (142.25 g). Stir at a heating temperature of 75 ° C for 7 hours.

[0081] In step (2), mesoporous silica and 3-mercaptopropyltrimethoxysilane (mass ratio is 7:1) are reacted at a heating temperature of 65° C. for 7 h to obtain modified mesoporous silica.

[0082] In step (3), after adding 40 wt% of hydrogen peroxide in the total reaction system, the reaction time is 22 hours. The centrifuged product is placed in an oven and dried for 10 hours to obtain 1 μm sulfonated mesoporous silica.

[0083] Example 3

[0084] This embodiment provides a 2 μm mesoporous silica catalyst and a preparation method thereof, and the specific implementation method is the same as that of Example 1; the difference is that:

[0085] In step (1), the amount of tetraethyl orthosilicate is 7.5g (3wt%), the surfactant is 0.375g of ethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) and 0.125g of ethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (F127) (total amount 0.2wt%), the nucleating modifier is barium chloride, the amount is 43g (17.2wt%), the amount of ammonia water is 62.5g (25wt%), and the rest is deionized water (136.5g). Stirring is carried out at a heating temperature of 65°C for 8h.

[0086] In step (2), mesoporous silica and 3-mercaptopropyltrimethoxysilane (mass ratio of 8:1) are reacted at a heating temperature of 60° C. for 6 h to obtain modified mesoporous silica. After centrifugation, the mesoporous silica is dried in a forced air drying oven at 60° C. for 9 h.

[0087] In step (3), after adding 40 wt% of hydrogen peroxide in the total reaction system, the reaction time is 20 h. The centrifuged product is placed in an oven and dried for 9 h to obtain 2 μm sulfonated mesoporous silica.

[0088] Comparative Example 1

[0089] This comparative example provides a 0.1 μm mesoporous silica catalyst and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that:

[0090] In step (1), the amount of ethyl silicate is 5.125 g (2.05 wt%), the surfactant is hexadecyltrimethylammonium bromide, the amount of which is 2.5 g (1.0 wt%), the amount of sodium chloride is 21.25 g (8.5 wt%), and the amount of deionized water is 133.625 g.

[0091] In step (2), the mass ratio of mesoporous silica to 3-mercaptopropyltrimethoxysilane is 4:1, and the reaction is carried out for 12 hours to obtain modified mesoporous silica.

[0092] In step (3), 50 wt% of hydrogen peroxide was added to the total reaction system, and the reaction time was 28 h. The centrifuged product was placed in an oven and dried for 12 h to obtain 0.5 μm sulfonated mesoporous silica.

[0093] Comparative Example 2

[0094] This comparative example provides a 4 μm mesoporous silica catalyst and a preparation method thereof. The specific implementation method is the same as that of Example 3, except that:

[0095] In step (1), the amount of tetraethyl orthosilicate is 10.0g (4.0wt%), the amount of surfactant is 0.1g of ethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) and the amount of ethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (F127) is 0.275g (total amount 0.15wt%), the amount of nucleating modifier is 45g (18.0wt%) of barium chloride, the amount of ammonia water is 50g (20wt%), and the amount of deionized water is 144.625g. Stirring is carried out at a heating temperature of 60°C for 10h.

[0096] In step (2), mesoporous silica and 3-mercaptopropyltrimethoxysilane (mass ratio of 10:1) are reacted at a heating temperature of 40° C. for 12 h to obtain modified mesoporous silica, which is then centrifuged and dried for 8 h.

[0097] In step (3), 40 wt% of hydrogen peroxide is added to the total reaction system, and the reaction time is 15 h.

[0098] Comparative Example 3

[0099] This comparative example provides a non-porous structure 0.5 μm silica catalyst and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that:

[0100] In step (1), the amount of ethyl silicate used is 5.125 g (2.05 wt%), no surfactant is used, the nucleation modifier is potassium chloride used in an amount of 12.5 g (5.0 wt%), and the amount of deionized water used is 144.875 g.

[0101] In step (2), the mass ratio of mesoporous silica to 3-mercaptopropyltrimethoxysilane is 13:1, and the reaction is carried out for 9 hours to obtain modified mesoporous silica.

[0102] In step (3), 45 wt% of hydrogen peroxide was added to the total reaction system, and the reaction time was 20 h. The centrifuged product was placed in an oven and dried for 12 h to obtain 0.5 μm sulfonated non-porous silica.

[0103] Comparative Example 4

[0104] This comparative example provides a low sulfonation degree 0.5 μm mesoporous silica catalyst and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that:

[0105] In step (2), the mass ratio of mesoporous silica to 3-mercaptopropyltrimethoxysilane is 12:1.

[0106] Comparative Example 5

[0107] This comparative example provides a low sulfonation degree 2 μm mesoporous silica catalyst and a preparation method thereof. The specific implementation method is the same as that of Example 3, except that:

[0108] In step (2), the mass ratio of mesoporous silica to 3-mercaptopropyltrimethoxysilane is 16:1.

[0109] The test results of the above embodiments and comparative embodiments are summarized in the following table:

[0110] Table 1

[0111]

[0112]

[0113] Note: Acid value (mgKOH / g) is the number of milligrams of potassium hydroxide (KOH) required to neutralize 1g of chemical substance, which can be used to indicate the amount of sulfonic acid groups loaded. The higher the acid value, the higher the loading amount.

[0114] According to Table 1, the 0.5-2 μm sulfonated mesoporous silica catalyst applied for in the present invention has obvious specific surface area advantages and pore structure advantages over the 0.1 μm, 0.5 μm, 2 μm, and 4 μm silica catalysts of the same type.

[0115] The huge specific surface area and abundant pore sizes enable the extremely high active group loading capacity applied for in the present invention to be expressed by acid value. The acid value of the catalyst is >357.781 mgKOH / g, which is higher than the acid value of traditional catalysts such as p-toluenesulfonic acid 326.1627 mgKOH / g.

[0116] At the same time, since the active groups of the 0.5-2 μm sulfonated mesoporous silica catalyst applied for in the present invention are stably covalently bonded to the matrix, the failure temperature of the active groups is above 190° C., which is much higher than the production requirement (160° C.).

[0117] Application Example 1

[0118] This application example provides a method for preparing tributyl aconitate catalyzed by a 0.5 μm mesoporous silica catalyst, and the preparation steps are as follows:

[0119] (1) Aconitic acid and n-butanol were mixed at a molar ratio of 1:3, and 0.4 parts by mass of a 0.5 μm mesoporous silica catalyst (derived from Example 1) was added to the mixed system (based on the total mass of aconitic acid and alcohol as 100 parts by mass), and the mixture was mixed evenly.

[0120] (2) The above system is heated at 120° C. and stirred for 4 hours to obtain tributyl aconitate.

[0121] (3) After the reaction is completed, the catalyst is separated and recovered by filtration, and then put into the reaction system again according to steps (1) and (2) for reaction, and is reused 5 times in total.

[0122] Application Example 2

[0123] This application example provides a method for preparing trimethyl aconitate catalyzed by a 1 μm mesoporous silica catalyst, and the preparation steps are as follows:

[0124] (1) Aconitic acid and methanol were mixed at a molar ratio of 1:4, and 0.4 parts by mass of a 1 μm mesoporous silica catalyst (from Example 2) was added to the mixed system (based on the total mass of aconitic acid and alcohol as 100 parts by mass), and the mixture was mixed evenly.

[0125] (2) The above system is heated at 100° C. and stirred for 4 hours to obtain trimethyl aconitate.

[0126] (3) After the reaction is completed, the catalyst is separated and recovered by filtration, and then put into the reaction system again according to steps (1) and (2) for reaction, and is reused 5 times in total.

[0127] Application Example 3

[0128] This application example provides a method for preparing tri(2-ethylhexyl)aconitate by catalysis of a 2 μm mesoporous silica catalyst, as follows:

[0129] (1) Aconitic acid and 2-ethylhexanol were mixed in a molar ratio of 1:3, and 5 parts by mass of a 2 μm mesoporous silica catalyst (derived from Example 3) was added to the mixed system (based on the total mass of aconitic acid and alcohol as 100 parts by mass), and the mixture was mixed evenly.

[0130] (2) The above system was heated at 145° C. and stirred for 6 hours to obtain tri(2-ethylhexyl)aconitate.

[0131] (3) After the reaction is completed, the catalyst is separated and recovered by filtration, and then put into the reaction system again according to steps (1) and (2) for reaction, and is reused 5 times in total.

[0132] Application Example 4

[0133] This application example provides a 0.5 μm mesoporous silica catalyst for catalytic preparation of trioctyl aconitate, and the steps are as follows:

[0134] (1) Aconitic acid and n-octanol were mixed at a molar ratio of 1:4, and 0.4 parts by mass of a 0.5 μm mesoporous silica catalyst (derived from Example 1) was added to the mixed system (based on the total mass of aconitic acid and alcohol as 100 parts by mass), and the mixture was mixed evenly.

[0135] (2) The above system is heated at 145° C. and stirred for 4 hours to obtain trioctyl aconitate.

[0136] (3) After the reaction is completed, the catalyst is separated and recovered by filtration, and then put into the reaction system again according to steps (1) and (2) for reaction, and is reused 5 times in total.

[0137] Application Example 5

[0138] This application example provides a 2 μm mesoporous silica catalyst for catalytic preparation of tridodecyl aconitate, and the steps are as follows:

[0139] (1) Aconitic acid and n-dodecanol were mixed at a molar ratio of 1:5, and 8 parts by mass of a 2 μm mesoporous silica catalyst (derived from Example 3) was added to the mixed system (based on the total mass of aconitic acid and alcohol as 100 parts by mass), and the mixture was mixed evenly.

[0140] (2) The above system is heated at 140° C. and stirred for 8 hours to obtain tridecyl aconitate.

[0141] (3) After the reaction is completed, the catalyst is separated and recovered by filtration, and then put into the reaction system again according to steps (1) and (2) for reaction, and is reused 5 times in total.

[0142] Application Example 6

[0143] This application example provides a 2 μm mesoporous silica catalyst for catalytic preparation of butyl octyl aconitate, and the steps are as follows:

[0144] (1) Aconitic acid, n-butanol and n-octanol were mixed in a molar ratio of 1:3:3, and 8 parts by mass of a 2 μm mesoporous silica catalyst (derived from Example 3) was added to the mixed system (based on the total mass of aconitic acid and alcohols as 100 parts by mass), and the mixture was mixed evenly.

[0145] (2) The above system is heated at 135° C. and stirred for 8 hours to obtain butyl octyl aconitate.

[0146] (3) After the reaction is completed, the catalyst is separated and recovered by filtration, and then put into the reaction system again according to steps (1) and (2) for reaction, and is reused 5 times in total.

[0147] Application Example 7

[0148] This application example provides a 0.5 μm mesoporous silica catalyst for catalytic preparation of trioctyl citrate, as follows:

[0149] (1) Citric acid and n-octanol were mixed at a molar ratio of 1:3, and 0.4 parts by mass of a 0.5 μm mesoporous silica catalyst (derived from Example 1) was added to the mixed system (based on the total mass of aconitic acid and alcohol as 100 parts by mass), and the mixture was mixed evenly.

[0150] (2) The above system is heated at 140° C. and stirred for reaction for 4 h to obtain trioctyl citrate.

[0151] (3) After the reaction is completed, the catalyst is separated and recovered by filtration, and then put into the reaction system again according to steps (1) and (2) for reaction, and is reused 5 times in total.

[0152] Application Example 8

[0153] This application example provides a 2μm mesoporous silica catalyst for catalytic preparation of tridodecyl citrate, the steps are as follows:

[0154] (1) Citric acid and n-dodecanol were mixed at a molar ratio of 1:5, and 8 parts by mass of a 2 μm mesoporous silica catalyst (derived from Example 3) was added to the mixed system (based on the total mass of aconitic acid and alcohol as 100 parts by mass), and the mixture was mixed evenly.

[0155] (2) The above system is heated at 135° C. and stirred for 7 hours to obtain tridecyl citrate.

[0156] (3) After the reaction is completed, the catalyst is separated and recovered by filtration, and then put into the reaction system again according to steps (1) and (2) for reaction, and is reused 5 times in total.

[0157] Comparative application example 1

[0158] This comparative application example provides a 2μm mesoporous silica catalyst for catalytic preparation of ethyl acetate, as follows:

[0159] (1) Acetic acid and ethanol were mixed in a molar ratio of 1:2, and 4 parts by mass of a 2 μm mesoporous silica catalyst (derived from Example 3) was added to the mixed system (based on the total mass of aconitic acid and alcohol as 100 parts by mass), and the mixture was mixed evenly.

[0160] (2) Heat the above system at 65° C. and stir the reaction for 4 h to obtain ethyl acetate.

[0161] (3) After the reaction is completed, the catalyst is separated and recovered by filtration, and then put into the reaction system again according to steps (1) and (2) for reaction, and is reused 5 times in total.

[0162] Comparative Application Example 2

[0163] This comparative application example provides a method for preparing dioctyl adipate catalyzed by a 1 μm mesoporous silica catalyst, and the preparation steps are as follows:

[0164] (1) Adipic acid and n-octanol were mixed at a molar ratio of 1:2.5, and 0.2 parts by mass of a 1 μm mesoporous silica catalyst (derived from Example 2) was added to the mixed system (based on the total mass of aconitic acid and alcohol as 100 parts by mass), and the mixture was mixed evenly.

[0165] (2) The above system is heated at 120° C. and stirred for reaction for 2 h to obtain dioctyl adipate.

[0166] (3) After the reaction is completed, the catalyst is separated and recovered by filtration, and then put into the reaction system again according to steps (1) and (2) for reaction, and is reused 5 times in total.

[0167] Comparative Application Example 3

[0168] This comparative application example provides a method for preparing dioctyl phthalate catalyzed by a 1 μm mesoporous silica catalyst, and the preparation steps are as follows:

[0169] (1) Phthalic anhydride and n-octanol were mixed at a molar ratio of 1:2.5, and 0.3 parts by mass of a 1 μm mesoporous silica catalyst (derived from Example 2) was added to the mixed system (based on the total mass of aconitic acid and alcohol as 100 parts by mass), and the mixture was mixed evenly.

[0170] (2) The above system is heated at 150° C. and stirred for 4 hours to obtain dioctyl phthalate.

[0171] (3) After the reaction is completed, the catalyst is separated and recovered by filtration, and then put into the reaction system again according to steps (1) and (2) for reaction, and is reused 5 times in total.

[0172] Comparative Application Example 4

[0173] This comparative application example provides a method for preparing trioctyl aconitate catalyzed by a 0.1 μm mesoporous silica catalyst, and the preparation steps are as follows:

[0174] (1) Aconitic acid and n-octanol were mixed in a molar ratio of 1:4, and 5 parts by mass of a 0.1 μm non-porous silica catalyst (derived from Comparative Example 1) was added to the mixed system (based on the total mass of aconitic acid and alcohol as 100 parts by mass), and the mixture was mixed evenly.

[0175] (2) The above system is heated at 145° C. and stirred for 4 hours to obtain trioctyl aconitate.

[0176] (3) After the reaction is completed, the catalyst is separated and recovered by filtration, and then put into the reaction system again according to steps (1) and (2) for reaction, and is reused 5 times in total.

[0177] Comparative Application Example 5

[0178] This comparative application example provides a method for preparing trioctyl aconitate catalyzed by 4 μm mesoporous silica, and the preparation steps are as follows:

[0179] (1) Aconitic acid and n-octanol were mixed at a molar ratio of 1:4, and 10 parts by mass of a 4 μm mesoporous silica catalyst (from Comparative Example 2) was added to the mixed system (based on the total mass of aconitic acid and alcohol as 100 parts by mass), and the mixture was mixed evenly.

[0180] (2) The above system is heated at 145° C. and stirred for 4 hours to obtain trioctyl aconitate.

[0181] (3) After the reaction is completed, the catalyst is separated and recovered by filtration, and then put into the reaction system again according to steps (1) and (2) for reaction, and is reused 5 times in total.

[0182] Comparative Application Example 6

[0183] This comparative application example provides a method for preparing trioctyl aconitate catalyzed by a 0.5 μm silica catalyst with a non-porous structure, and the preparation steps are as follows:

[0184] (1) Aconitic acid and n-octanol were mixed at a molar ratio of 1:4, and 5 parts by mass of a non-porous 0.5 μm silica catalyst (derived from Comparative Example 3) was added to the mixed system (based on the total mass of aconitic acid and alcohol as 100 parts by mass), and the mixture was mixed evenly.

[0185] (2) The above system is heated at 145° C. and stirred for 4 hours to obtain trioctyl aconitate.

[0186] (3) After the reaction is completed, the catalyst is separated and recovered by filtration, and then put into the reaction system again according to steps (1) and (2) for reaction, and is reused 5 times in total.

[0187] Comparative Application Example 7

[0188] This comparative application example provides a method for preparing trioctyl aconitate catalyzed by a low-sulfonation degree 0.5 μm mesoporous silica catalyst, and the preparation steps are as follows:

[0189] (1) Aconitic acid and n-octanol were mixed at a molar ratio of 1:4, and 0.4 parts by mass of a low-sulfonation degree 0.5 μm mesoporous silica catalyst (derived from Comparative Example 4) was added to the mixed system (based on the total mass of aconitic acid and alcohol as 100 parts by mass), and the mixture was mixed evenly.

[0190] (2) The above system is heated at 145° C. and stirred for 4 hours to obtain trioctyl aconitate.

[0191] (3) After the reaction is completed, the catalyst is separated and recovered by filtration, and then put into the reaction system again according to steps (1) and (2) for reaction, and is reused 5 times in total.

[0192] Comparative Application Example 8

[0193] This comparative application example provides a method for preparing trioctyl aconitate catalyzed by a low-sulfonation degree 2μm mesoporous silica catalyst, and the preparation steps are as follows:

[0194] (1) Aconitic acid and n-octanol were mixed at a molar ratio of 1:4, and 10 parts by mass of a low-sulfonation degree 2 μm mesoporous silica catalyst (from Comparative Example 5) was added to the mixed system (based on the total mass of aconitic acid and alcohol as 100 parts by mass), and the mixture was mixed evenly.

[0195] (2) The above system is heated at 145° C. and stirred for 4 hours to obtain trioctyl aconitate.

[0196] (3) After the reaction is completed, the catalyst is separated and recovered by filtration, and then put into the reaction system again according to steps (1) and (2) for reaction, and is reused 5 times in total.

[0197] Comparative Application Example 9

[0198] This comparative application example provides a method for preparing trioctyl aconitate catalyzed by concentrated sulfuric acid, and the preparation steps are as follows:

[0199] (1) Aconitic acid and n-octanol are mixed at a molar ratio of 1:4, and 3 parts by mass of a 98.3% concentrated sulfuric acid aqueous solution are added to the mixed system (based on the total mass of aconitic acid and alcohol as 100 parts by mass) and mixed evenly.

[0200] (2) The above system is heated at 100° C. and stirred for 6 hours to obtain trioctyl aconitate.

[0201] (3) After the reaction is completed, the reaction system is subjected to an alkali neutralization operation to remove the concentrated sulfuric acid aqueous solution to obtain a product.

[0202] Comparative Application Example 10

[0203] This comparative application example provides a method for preparing trioctyl aconitate catalyzed by concentrated hydrochloric acid, and the preparation steps are as follows:

[0204] (1) Aconitic acid and n-octanol are mixed at a molar ratio of 1:4, and 3 parts by mass of a 98.3% concentrated hydrochloric acid aqueous solution are added to the mixed system (based on the total mass of aconitic acid and alcohol as 100 parts by mass) and mixed evenly.

[0205] (2) The above system is heated at 125° C. and stirred for 4 hours to obtain trioctyl aconitate.

[0206] (3) After the reaction is completed, the reaction system is subjected to an alkali neutralization operation to remove the concentrated hydrochloric acid aqueous solution to obtain the product.

[0207] Comparative Application Example 11

[0208] This comparative application example provides a method for preparing trioctyl aconitate catalyzed by sodium bisulfate, and the preparation steps are as follows:

[0209] (1) Aconitic acid and n-octanol are mixed at a molar ratio of 1:4, and 4 parts by mass of a sodium bisulfate catalyst with a purity of 99% is added to the mixed system (based on the total mass of aconitic acid and alcohol as 100 parts by mass) and mixed evenly.

[0210] (2) The above system is heated at 130° C. and stirred for 4 hours to obtain trioctyl aconitate.

[0211] (3) After the reaction is completed, the sodium bisulfate is separated by filtration, and then the reaction system is washed and extracted to obtain the product.

[0212] Comparative Application Example 12

[0213] This comparative application example provides a method for preparing trioctyl aconitate catalyzed by tetrabutyl titanate, and the preparation steps are as follows:

[0214] 1) Aconitic acid and n-octanol are mixed in a molar ratio of 1:4, and 0.5 parts by mass of tetrabutyl titanate catalyst with a purity of 99% is added to the mixed system (based on the total mass of aconitic acid and alcohol as 100 parts by mass) and mixed evenly.

[0215] (2) The above system is heated at 200° C. and stirred for 4 hours to obtain trioctyl aconitate.

[0216] (3) After the reaction is completed, the reaction system is subjected to a washing and extraction operation to remove tetrabutyl titanate to obtain a product.

[0217] Comparative Application Example 13

[0218] This comparative application example provides a method for preparing trioctyl citrate catalyzed by concentrated sulfuric acid, and the preparation steps are as follows:

[0219] (1) citric acid and n-octanol are mixed at a molar ratio of 1:4, and 3 parts by mass of a 98.3% concentrated sulfuric acid aqueous solution are added to the mixed system (based on the total mass of aconitic acid and alcohol as 100 parts by mass) and mixed evenly.

[0220] (2) The above system is heated at 100° C. and stirred for 6 hours to obtain trioctyl citrate.

[0221] (3) After the reaction is completed, the reaction system is subjected to an alkali neutralization operation to remove the concentrated sulfuric acid aqueous solution to obtain a product.

[0222] Comparative Application Example 14

[0223] This comparative application example provides a method for preparing trioctyl citrate catalyzed by concentrated hydrochloric acid, and the preparation steps are as follows:

[0224] (1) citric acid and n-octanol are mixed at a molar ratio of 1:4, and 3 parts by mass of a 98.3% concentrated hydrochloric acid aqueous solution are added to the mixed system (based on the total mass of aconitic acid and alcohol as 100 parts by mass) and mixed evenly.

[0225] (2) The above system is heated at 125° C. and stirred for reaction for 4 h to obtain trioctyl citrate.

[0226] (3) After the reaction is completed, the reaction system is subjected to an alkali neutralization operation to remove the concentrated hydrochloric acid aqueous solution to obtain the product.

[0227] The test results of the above application examples and comparative application examples are summarized in the following table:

[0228] Table 2

[0229]

[0230]

[0231] The data and technical effects in Table 2 are summarized as follows:

[0232] (1) Catalysis of single aconitate: According to Application Examples 1-5, the 0.5-2 μm sulfonated mesoporous silica catalyst applied in the present invention can stably catalyze the esterification reaction of alcohols from C1 to C12 with tricarboxylic acids, overcoming the large steric hindrance effect. As in Application Example 5, the 2 μm sulfonated mesoporous silica catalyst with the largest particle size and the smallest specific surface area catalyzed tridecyl aconitate, and the initial conversion rate reached 95%.

[0233] At the same time, after being recycled and reused for 5 times, the average conversion rate of the target product prepared by the catalysts of various particle sizes was above 94%, which proves that the sulfonated mesoporous silica catalyst applied for in the present invention has extremely high catalytic efficiency and stable performance.

[0234] (2) Catalysis of mixed esters of aconitic acid: According to Application Example 6, the conversion rate of the target product prepared by the sulfonated mesoporous silica catalyst applied in the present invention reached 87% after being recycled for 5 times, and the initial catalytic conversion rate was as high as 96%, which proves that the sulfonated mesoporous silica catalyst applied in the present invention can further overcome the difficulty of the large steric hindrance esterification reaction in the production of mixed esters and expand the types of mixed esters.

[0235] (3) Catalysis of single citrate ester: According to Application Examples 7-8, the sulfonated mesoporous silica catalyst applied in the present invention has an initial 4h triester conversion rate of more than 96% for the citric acid esterification reaction, and the average triester conversion rate after 5 cycles has reached more than 95%. Compared with Application Examples 1 and 5, the triester conversion rate of single citrate ester is slightly higher, which shows that the carbon-carbon conjugated double bonds contained in aconitic acid do enhance the rigidity of the main body of the aconitic acid molecule, making the molecular chain connected to the double bond less likely to rotate and the esterification reaction less likely to proceed. However, the experimental results of the application examples prove that the sulfonated mesoporous silica catalyst described in the present application has a flexible and controllable particle size and extremely rich active sites, so that it can more fully contact the various carboxylic acid groups of aconitic acid and citric acid during the catalytic esterification of citric acid and aconitic acid, promote the esterification process, and then accelerate the reaction process and improve the conversion rate.

[0236] (4) Catalysis of dicarboxylic acid esters: According to comparative application examples 1-3, when the sulfonated mesoporous silica catalyst of the present invention is used to catalyze the preparation of dicarboxylic acid esters, the initial conversion rate of each dicarboxylic acid ester is higher than 96%, and the average conversion rate after 5 cycles is also higher than 94%. This proves that the sulfonated mesoporous silica catalyst of the present invention has the basic performance of efficiently catalyzing the preparation of dicarboxylic acid esters.

[0237] (5) Compared with other silica catalysts of the same type: According to comparative application examples 4-8, when catalyzing the preparation of trioctyl aconitate with large steric hindrance, the larger the specific surface area of ​​the catalyst, the more active groups loaded, and the higher the catalytic efficiency when catalyzing the esterification reaction. At the same time, the particle size will also affect the recycling performance of the catalyst, especially the time cost. The larger the particle size, the easier it is to separate the catalyst. According to comparative application example 4, although the 0.1μm sulfonated silica catalyst has the best catalytic effect, the filtration operation required for separation is more delicate and takes longer, which reduces the recycling performance. The 0.5-2μm sulfonated mesoporous silica catalyst provided by the present invention not only ensures a higher catalytic efficiency, but also ensures that the production has a suitable time cost.

[0238] (6) Compared with other general catalysts: According to comparative application examples 9-12, when the catalyst is replaced with concentrated sulfuric acid, concentrated hydrochloric acid, sodium bisulfate and tetrabutyl titanate, the initial 4h triester conversion rate of the tricarboxylic acid aconitic acid is less than 86%, and the esterification catalytic efficiency is low. The reason is the same as above. Aconitic acid has one more carbon-carbon conjugated double bond than citric acid. The conjugated double bond greatly improves the rigidity of the main structure of the aconitic acid molecule, and the molecular chain connected to the double bond is less likely to rotate. Therefore, the mobility of the carboxyl group around the carbon-carbon double bond is also reduced, and the chance of contact with the catalyst is reduced, resulting in the esterification reaction being more difficult to proceed; at the same time, general esterification catalysts such as concentrated sulfuric acid and concentrated hydrochloric acid are not reusable, so the catalyst cannot be recovered after the reaction is completed. It is proved that the sulfonated mesoporous silica catalyst applied by the present invention has higher esterification catalytic activity and green environmental protection and reusable characteristics for aconitic acid than general catalysts.

[0239] (7) Compared with other general-purpose catalyst-catalyzed citric acid esterification systems: According to comparative application examples 13-14, when the tricarboxylic acid is replaced by citric acid and the catalyst is replaced by concentrated sulfuric acid and concentrated hydrochloric acid, the initial 4h triester conversion rate of the tricarboxylic acid citric acid is below 91%, which is slightly higher than the esterification efficiency of aconitic acid under the same system (comparative application examples 9-10), which further indirectly illustrates that the carbon-carbon conjugated double bond on aconitic acid plays an important role in the structural stability of aconitic acid; while citric acid does not have a carbon-carbon conjugated double bond, but is replaced by a carbon-carbon single bond and a single hydroxyl group, which makes the structural stability of citric acid lower than that of aconitic acid, and the molecular chain mobility is relatively high, and the three carboxyl groups contained therein have more opportunities to contact the catalyst, so the esterification reaction of citric acid is easier to proceed than that of aconitic acid. Therefore, the esterification of citric acid catalyzed by concentrated sulfuric acid and concentrated hydrochloric acid has a slightly higher esterification conversion rate.

[0240] The above is only an example of the present application, and the protection scope of the present application is not limited by these specific embodiments, but is determined by the claims of the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the technical ideas and principles of the present application should be included in the protection scope of the present application.

Claims

1. A mesoporous silica catalyst for catalyzing the esterification reaction of tricarboxylic acids, characterized in that: The catalyst is composed of a mesoporous silica matrix and a surface-modified loaded organic functional group; the particle size of the silica matrix is ​​distributed between 0.5 and 2 μm, and the specific surface area of ​​the silica matrix is ​​302-569 m 2 / g, the most probable pore sizes are 1-10nm and 20-100nm, and the heat-resistant temperature is above 190℃.

2. The method for preparing a mesoporous silica catalyst for catalyzing the esterification reaction of tricarboxylic acids according to claim 1, characterized in that: The following steps are involved: (1) Preparation of mesoporous silica: using silane as raw material, deionized water as solvent, surfactant as micelle template, inorganic salt as nucleation modifier, under the catalysis of alkaline catalyst, heating and stirring to obtain mesoporous silica; Wherein, the silane includes at least one of tetraethyl orthosilicate, tetrapropyl orthosilicate, tetrabutoxysilane, methyltriethoxysilane, dimethyldiethoxysilane or ethyl polysilicate; the surfactant micelle includes at least one of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, and hexadecyltrimethylammonium toluenesulfonate; the alkaline catalyst includes ammonia water, triethanolamine, ethylamine, propylamine, butylamine, diethylamine, diethylamine or triethylamine; the inorganic salt includes at least one of potassium chloride, sodium chloride, barium chloride, ferric chloride, and calcium chloride; (2) Purification and modification of mesoporous silica: The mesoporous silica is purified by centrifugal washing and then dried; after drying, the average particle size of the mesoporous silica is 500-2 μm, and the specific surface area is 302-569 m 2 / g; using deionized water as solvent, dispersing the dried mesoporous silica in water by ultrasound to obtain a uniform silica solution; then adding 3-mercaptopropyltrimethoxysilane thereto, heating the reaction for a certain period of time to obtain a modified mesoporous silica solution; (3) Sulfonation of modified mesoporous silica: hydrogen peroxide is added to the modified mesoporous silica solution to carry out stirring reaction, and after the reaction is completed, centrifugation is performed to obtain a centrifuged product, and the centrifuged product is placed in an oven to dry to obtain dry sulfonated mesoporous silica.

3. The method for preparing a mesoporous silica catalyst for catalyzing the esterification reaction of tricarboxylic acids according to claim 2, characterized in that: In step (1), the amount of silane is 2.4-3.3wt%, the amount of surfactant is 0.15wt%-0.8wt%, the amount of alkaline catalyst is 22-35wt%, the amount of inorganic salt is 5.0-18wt%, the heating temperature is 60-85°C, and the stirring time is 4-8h.

4. The method for preparing the mesoporous silica catalyst for catalyzing the esterification reaction of tricarboxylic acids according to claim 2, characterized in that: In step (2), deionized water or ethanol is used as a washing liquid, the centrifuge speed is 1000-1800 rpm, the centrifugation time is 5-10 min, and the centrifugation is performed 5 times; after centrifugation, the mixture is placed in a 50-60° C. forced air drying oven for 8-12 h to remove the micelle agent; deionized water is used as a solvent in the ultrasonic dispersion, and the mass ratio of mesoporous silica to 3-mercaptopropyltrimethoxysilane is (5-8):1; the reaction temperature is 40-75° C., and the reaction time is 6-10 h.

5. The method for preparing the mesoporous silica catalyst for catalyzing the esterification reaction of tricarboxylic acids according to claim 2, characterized in that: In step (3), the amount of hydrogen peroxide is 35-45wt%, the reaction time is 12-28h under heating and stirring, the centrifuge speed is 1000-2000rpm, the centrifugation time is 5-10min, the centrifugation is performed 5 times, the detergent is deionized water or ethanol, the drying temperature after centrifugation is 50-80°C, and the drying time is 8-12h.

6. Use of the mesoporous silica catalyst according to claim 1 in catalyzing the esterification reaction of tricarboxylic acids.

7. A method for preparing a tricarboxylic acid ester, characterized in that: The preparation method comprises: in the presence of the mesoporous silica catalyst described in claim 1, under heating conditions, mixing a tricarboxylic acid and an alcohol, and allowing the mixture to react for a certain period of time to obtain a tricarboxylic acid ester; after the reaction, separating the catalyst by a separation operation, washing and drying it, and using it for the next reaction.

8. The method for preparing a tricarboxylic acid ester according to claim 7, wherein: The tricarboxylic acid is at least one of citric acid and aconitic acid; the alcohol is methanol, ethanol, 2-methoxyethanol, 2-ethoxyethanol, propanol, isopropanol, n-butanol, isobutanol, tert-butanol, n-pentanol, isopentanol, tert-pentanol, 2-methylpentanol, 2-methyl-2-pentanol, 2-methyl-3-pentanol, 3-ethyl-3-pentanol, 4-methyl-1-pentanol, 4-methyl-2-pentanol, n-hexanol, 2-hexanol, 3-hexanol, 2-ethylhexanol, 3,5,5-trimethylhexanol, n-heptanol, 2 -heptanol, 3-heptanol, 2-methylheptanol, 4-methyl-3-heptanol, 3-propylheptanol, 2,6-dimethyl-4-heptanol, n-octanol, 2-octanol, n-nonanol, 2-nonanol, 3-nonanol, 5-ethyl-2-nonanol, 2,6,8-trimethyl-4-nonanol, n-decanol, isodecanol, n-undecanol, and n-dodecanol; the heating temperature is 50-170° C.; the reaction time is 4-14 h; the separation operation comprises at least one of static sedimentation, centrifugation, suction filtration, and filtration.

9. The method for preparing a tribasic carboxyl ester according to claim 8, wherein: Based on 100 parts by mass of the total mass of the tricarboxylic acid and the alcohol, the added amount of the mesoporous silica catalyst is 0.3-10 parts by mass.

10. The method for preparing a tribasic carboxylic ester according to claim 8, wherein: The molar ratio of the tricarboxylic acid to the alcohol is 1:3-1:8, the heating temperature is 68-150° C., and the reaction time is 4-10 hours.

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